There are a number of surgical procedures which require the fixation of bones such as spinal fixation of portions of the spine with respect to one another or fixation of bone fragments as a result of trauma. Typically, bone bolts or screws and bone plates or spinal rods are employed in the fixation of bones wherein the bone bolts or screws are implanted in a surgical procedure involving the formation of a series of surgical openings in adjacent portions of the spine or along a bone, for implanting the threaded bone bolts or screws. Connective structures such as rods or plates extend between the various spine members or bone fragments and are connected to the implanted bolts or screws with connector devices.
A U.S. Pat. No. 4,369,769 to Edwards shows a spinal fixation system using elongated rods to bridge across various portions of the spine. In the Edwards '769 patent, a spinal fixation device is provided in which sleeves or spacers are placed over and around spinal rods in order to obtain a better reduction of spinal fractures or spinal deformities. These sleeves can be made into various thicknesses so that the surgeon can obtain optimum fixation in each case.
Use of bone screws in connecting rods is also seen in the Ulrich et al. U.S. Pat. No. 4,433,677 entitled "Implantable Splint for Correction of Lumbosacral Spondylodesis." In the Ulrich patent, a spinal distraction splint has two like anchor screws extending along respective longitudinal screw axes and adapted to be anchored in the pelvis with the axes crossing. Each of the screws has a head formed with a transverse open recess centered on respective transverse axis and with an angular array of teeth centered on and angularly spaced about the respective transverse axis.
A U.S. Pat. No. 4,611,581 to Steffee entitled "Apparatus for Straightening Spinal Columns" provides an apparatus to reduce the extent of displacement between adjacent vertebrae and a person's spinal column and to subsequently maintain the vertebrae in a reduced displacement relationship. When the apparatus is to be installed, holes are formed in the displaced vertebrae and in vertebrae on opposite sides of the displaced vertebrae. Force transmitting members (bone bolts) are mounted in the holes in the vertebrae. A spinal plate is then positioned on the spinal column with the bone bolts extending outwardly through the slots in the spinal plate. Nuts are tightened on the bone bolt members connected with vertebrae on opposite sides of the displaced vertebrae to anchor the spinal plate in place. A nut on the extending bone bolt is then tightened to hold the displaced vertebrae in the desired position. Connectors for attaching the rods or plates to vertebrae of a spinal column are known in the art, for example such as those described in U.S. Pat. Nos. 5,209,752 and 5,296,014.
When doctors use a plurality of bone bolts implanted in a series of bolts, and desire a connection of the series, it is frequently difficult to make a tight connection because of the non-alignment of the series. For example, in a spinal construct where bone bolts are placed in several adjacent vertebral pedicles, the adjacent bone bolts will almost never align themselves such that a plate or rod may be connected to them. The adjacent bone screws are usually independently located with respect to each other in three dimensional space, which creates an offset distance of some kind between the bolt and the plate/rod connection. The offset problem has been addressed by providing connectors that accommodate the differences of the adjacent bolts implanted in a series. However, there is a limit to the adjustability of the currently available connectors when used with traditional bone bolts and bone screws.
In order to accommodate the differing spinal vertebrae of many patients and to provide a fixation system in which a series of implanted bone bolts can be aligned so as to provide adjustment for the three dimensional differences in the implanted bolts, a medical device such as a multi-angle bone bolt is needed that allows for variability in both placement and angulation of upper and lower portions of the bolt in order to provide an effective bone fixation system.
A multi-angle bone bolt is also needed for use in any bone fixation system in which uneven bone portions are connected to a connecting member where angulation of upper and lower portions of the bolt will provide a more effective and secure bone fixation system.